(11) Betas and their t-Stats
from the covar matrix of b=σ2(X'X)-1
the var(βi) = σ2vii where vii is the ith diag element of X'X-1
where σ2 = e'e / n-k (k=num of ind vars plus 1 for the intercept if present).
and where vii is the ith diag element of X'X-1
Std(βi) = sqr root of Var(βi)
TStat(βi) = βi / Std(βi)
Estimate of σ2 = 9.75302773800037